[Jay S]

I did a lot of research on the 500557 blocks. I don’t know of ANY mods to that guys turbo engine that would have ended much different, that was over 1000 HP! It will even be asking a lot out of an earlier heavier block if he doesn’t step up and add 4 bolt caps, preferably splayed.

For smaller HP builds, all the weak blocks I have seen that broke the main webbing out had dowel pins. The first year of production there was a lot of trouble with a crack starting at the dowel hole. The holes are drilled all the way thru, once a crack starts it will grow until the webbed breaks out. But, there have been a couple effective methods to stop a crack from starting.

The best modification I have seen, at least more most moderate street builds, is to increase the dowel size to 5/16”, and use a longer dowel the goes the FULL length of the dowel hole. That mod along with main studs using up to a 4” crank the block can take a good amount of HP.

I have found some builds machine the block to use 4 bolt main. The outside bolt’s are pretty short, it is pretty expensive for not a lot of improvement in strength. But it is probably a little stronger than the 2 bolt, it still needs the longer dowels.

Pontiac’s solution was to use roll pins or spring pins instead of solid dowels to index the main caps. The springs put an equal force on the drilled hole. This stopped the cracks that started at the dowels. But the problem they had is it didn’t index the caps enough. Those engines, with a good amount of abuse, have a tendency to spin main bearings.

For this engine I used a main girdle to support the main caps. It lowers the stock pan a 1/4”, but it uses a stock aftermarket oil pan. It adds another level of indexing to the mains. I kept the roll pins and it has ARP studs clamping the main caps on. I have another build similar to this one that has solid dowels and the full girdle.

This is my thoughts on power output on the weaker late 500557 400 blocks.

400 HP -Stock
500 HP—ARP studs, line honed, longer and enlarged dowels, 3.75” or 4” crank
600 HP, strokers, Full girdle, halos and pan rail supports, ARP’s, line honed
ARP main studs, line honed, full main girdle with